Halogen incandescent lamp

ABSTRACT

The halogen incandescent lamp has a tungsten filament and its halogen cycle takes place with fluorine participating therein. To prevent corrosive action of the fluorine on internal lamp components, the inert fill gas contains an additive of perhalogenated low molecular weight hydrocarbons with at least one fluorine atom per molecule in a concentration of from 1 X 10 8 to 1 X 10 6 gram atoms of fluorine, and from 1 X 10 8 to 1 X 10 6 gram atoms of at least one more halogen such as chlorine, bromine, or iodine per cc of bulb volume; preferably, difluorodibromomethane (CF2Br2) is admixed to the fill gas. During lamp operation, a cyclic tungsten-fluorine process takes place close to the filament, the tungsten not included in this cycle is transported back to the filament by the second halogen.

I United States Patent 91 [111 3,732,455 Neumann 1 May 8, 1973 [54]HALOGEN INCANDESCENT LAMP FOREIGN PATENTS OR APPLICATIONS 1 lnvemorlGerhard Neumann Munich, 954,729 4/1964 Great Britain ..313 223 Germany898,115 6/1962 Great Britain ..3l3/223 [73] Assignee:Patent-Treuhand-Gesellschaft fur elektrische, Munich, Germany Emmme RyLake Assistant ExaminerJames B. Mullms [22] Fled: 1971 Attorney-Flynn &Frishauf [2i] Appl. No.: 113,980

[57] ABSTRACT 30 Foreign Application p i i Data The halogen incandescentlamp has a tungsten filament and its halogen cycle takes place withfluorine Mar. 3,1970 Germany....- ..P 20 09 916.5 participatingtherfiirL To prevent corrosive action of the fluorine on internal lampcomponents, the inert fill [52] US. Cl ..313/222, 3 134222 gas containsan additive of perhalogenated low 2; molecular weight hydrocarbons withat least one 1 he 0 care l 31:; fluorine atom per molecule in aconcentration of from l X 10- to l X 10 gram atoms of fluorine, and from1 X 10' to I X 10 gram atoms of at least one more [56] References cuedhalogen such as chlorine, bromine, or iodine per cc of UNITED STATESPATENTS bulb volume; preferably, difluorodibromomethane (CF Br isadmixed to the fill gas. During lamp opera- 3 at 2 tion, a cyclictungsten-fluorine process takes place 3 3 1111970 z g i f g 31/312 Xclose to the filament, the tungsten not included in this cycle istransported back to the filament by the second halogen.

9 Claims, 1 Drawing Figure llllllllllr PATENTED 81375 3.732.455

Dr. Gerhard M. Neumann INVENTOR HALOGEN INCANDESCENT LAMP Incandescentelectric lamps having tungsten filaments and whose bulb filling of inertgases contains halogen additives are known in the art. With the aid of ahalogen additive, a cyclic process takes place inside the lamp duringoperation thereof, during which the tungsten particles evaporating offthe filament and normally depositing on the wall of the bulb areconverted at the operating temperature of the lamp envelope to gaseoustungsten halides and are transported back onto the filament. Thetungsten halides are decomposed close to the hot filament to freehalogens and tungsten, which is deposited onto the filament.Incandescent lamps having halogen additives in the fill gas do notblacken throughout their operating lives, and their light outputefficiency remains approximately constant during operational life.

The halogens iodine, bromine, chlorine or fluorine may be used for thedescribed cycle; gaseous mixtures of the halogens have been suggested.(See German Pat. publication No. 1.241.531). If fluorine is added to theinert fill gas of the lamp, the inner wall of the bulb and the othercomponents located inside the lamp, such as, for instance, the filamentsupports, have to be provided with a coating which isgaseous-fluorine-resistant. Also when using the other halogens, possibleattack by the free halogens on the filament ends, the metallic supportsand the lead-in wires must be prevented or, at least, delayed. Whenusing bromine, the simultaneous presence of hydrogen within the lamp hasproved suitable. The favorable effect of hydrogen is supposed to resultfrom the formation of hydrogen bromide, which inhibits an attack of theelementary bromine on the metallic components. Hydrocarbon brominecompounds are thus added to the inert fill gas supplying bromine andhydrogen (see German Patent publication paper No. 1.489.441).

From investigations of the fluorine cycle in halogen incandescent lampsit is known that with the normally used filament temperatures the rateof decomposition of the tungsten fluorides is higher than the rate ofevaporation of the tungsten filament. Consequently, in such a halogenincandescent lamp, the evaporated tungsten from the gaseous phase isconducted as a compound with fluorine to the hottest spots of thefilament and is deposited thereon. By this deposition of tungsten, thehottest spots are reinforced, and a temperature balance of the filamentis effected. Up to now, this advantage of the tungsten-fluorine cyclecould not be utilized, because extraordinarily complicated protectivemeasures were necessary to prevent an attack by the fluorine on thematerial of the envelope and on the internal lamp components.

It is an object of the present invention to provide a halogenincandescent lamp inside which, during operation the halogen cycle takesplace while fluorine is simultaneously present, without necessitatingspecial measures to protect the lamp bulb and also the internal lampcomponents from an attack by fluorine. Consequently, the inventionpermits the utilization of the known specific advantages of thetungsten-fluorine cycle, i.e. the redeposition of the evaporatedtungsten on the hottest spots of the filament.

The invention thus relates to a halogen incandescent lamp which has atungsten filament and an additive to the inert fill gas of compoundscontaining halogens, which during operation of the lamp supply fluorineand at least one more halogen to the halogen cycle to prevent blackeningof the lamp bulb.

Subject matter of the invention:

Perhalogenated low molecular weight hydrocarbons which contain at leastone fluorine atom per molecule, are admixed to the inert fill gas. Theamount of perhalogenated low molecular weight hydrocarbons admixed tothe inert fill gas and containing at least one fluorine atom permolecule is so determined that a concentration of from 1 X 10- to 1 X 10gram atoms of fluorine per cc of bulb volume and a concentration of from1 X 10- to 1 X 10' gram atoms of at least one more halogen per cc ofbulb volume is obtained. A concentration of from 7 X 10- to 4 X 10- gramatoms per cc of bulb volume and a concentration of from 7 X 10' to 4 X10- gram atoms of at least one more halogen per cc of bulb volume isespecially favorable. Preferably, perhalogenated methanes of the generalcomposition CF X are admixed to the inert fill gas, wherein X ischlorine and/or bromine and/or-iodine, m is a whole number at least 1,and n is a whole number at most 3, and the sum of m n equals 4. Alsoperhalogenated ethanes of the general composition C F X are suitable,wherein X is chlorine and/or bromine and/or iodine, p is a whole numberat least 1, q is a whole number at most 5, and the sum of p q equals 6.Most favorable results are obtained with admixtures ofdifluorodichloromethane (CF Cl and of difluoromonochloromonobromomethane(CF ClBr) and of difluorodibromomethane (CF Br to the fill gas, theaforesaid bromine-containing compounds being distinguished from thechlorine containing compounds in that they form during the dissociationwithin the lamp elemental bromine which is less corrosive with regard tometal parts. For this reason, the aforesaid bromine containing compoundsare preferably used, however, the chlorine containing compounds may alsobe used and furnish satisfactory results in lamps according to theinvention. Furthermore, trifluoromonochloromethane (CF Cltrifluoromonobromomethane (CF Br) monofluorotrichloromethane (CFClmonofluorotribromomethane (CFBr tetrafluorodibromoethane (C F Br andtrifluorotrichloroethane (C' F Cl and the corresponding perhalogenatedlow molecular weight hydrocarbons with atleast one fluorine atom permolecule containing iodine and chlorine, or bromine and, furthermore,containing chlorine and bromine, are satisfactory in use.

As used in this application, hydrocarbons with one and up to about fourhydrocarbon atoms per molecule are designated low molecular weighthydrocarbons.

the inert lamp fill gas in the required quantity without anytechnological difficulties.

Let it be assumed that the cyclic process within the incandescent lampduring operation thereof with the admixture of perhalogenatedhydrocarbons according to the invention with at least one fluorine atomper molecule to the inert fill gas, is caused by the chemically andthermally highly resistant compounds which dissociate to a very smallextent at above 2,000C close to the highly heated filament and thussupply a small amount of elementary fluorine besides the other halogenspresent in the molecule. in the presence of, for instance,difluorodibromomethane in the lamp bulb, there may occur the followingreversible disproportionation:

2 cigar, CF, CBr, 1

The resulting CF may then dissociate forming However, anotherdisproportionation appears to be possible also:

2CF Br cFBr l-CF Br 3 with the ensuing reactions under formation ofperhalogenated ethanes and of elementary halogens:

2 CFBr C,F,Br,+ 2 Br 4 and I 2 CF Br C F Br 2 F 5 2 CF Br C F Br 6 Stillmore conversions are conceivable, which explain the transient liberationof elementary fluorine and elementary bromine from thedifluorodibromomethane admixed to the inert fill gas, as indicated inthe equations 1 to 6. Similar considerations apply to perhalogenatedhydrocarbons with a higher or lower bromine component than that presentin difluorodibromomethane, and with at least one fluorine atom permolecule and, correspondingly, they also apply to perhalogenatedhydrocarbons with chlorine atoms and/or iodine atoms and, eventually inaddition, bromine atoms and with at least one fluorine atom permolecule. A theoretical thermodynamic explanation of the processesinside the bulb during operation of the lamp is difficult tohypothesise, however, it is not necessary for an understanding of thesubject matter of the invention.

According to the invention, the tungsten-halogen cycle in incandescentlamps preventing blackening can proceed with either fluorine or anotherhalogen such as, for instance, chlorine or bromine participatingtherein. It appears that the tungsten-fluorine cycle only takes placeclose to the filament. The surprising observation that no corrosion ofthe lamp bulb occurs during operation points in this direction. Thetungsten particles which are not included in the fluorine cycle, areconverted by the second halogen present in the lamp and are transportedback to the filament.

When using perhalogenated hydrocarbons with at least one fluorine atomas admixture to the inert fill gas, no other measures for protection ofthe components located inside the lamp, such asthe filament supports,are necessary. The regeneration of the chemically and thermally stableperhalogenated hydrocarbons from the transient dissociation products isconsequently rapid and complete.

The accompanying drawing shows a hologen incandescent lamp with anadditive to the inert fill gas of perhalogenated hydrocarbons comprisingat least one fluorine atom per molecule.

Tungsten filament 1 is located inside lamp envelope 2 of glass, which'may be, but need not be, quartz glass and is supported by supportingwires 3, 4. The supporting wires are connected with molybdenum foils 5,6, which are hermetically pinch-sealed into the glass, and to whichterminals 7, 8 are welded. The lamp is operated at 24 V and with a powerinput of 250 W. The lamp envelope contains a filling of inert gases,such as nitrogen, rare gases or mixtures thereof, and an admixture ofperhalogenated low hydrocarbons with at least one fluorine atom permolecule andin such a quantity that a concentration of from 1 X l0 to 1X 10' gram atoms of fluorine per cc of bulb volume and a concentrationof from 1 X 10' to l X 10' gram atoms of at least one more halogen percc of bulb volume results. Preferably, a concentration of from 7 X 10'to 4 X 10- gram atoms of fluorine per cc of bulb volume and from 7 X 1.0to 4 X 10 gram atoms of at least one more halogen per cc of bulb volumeis utilized. The cold fill pressure of the lamp may be, for instance, to660 torr or even more. f

The lamp envelope should be dimensioned so that during operation of thelamp a wall temperature of at least 250C is attained. Known high-meltingglasses, quartz glass hard glasses or even simple glass compositions canbe used for manufacturing the lamp envelope. The drawing shows asingle-ended halogen incandescent lamp, although the invention is alsoapplicable to halogen incandescent lamps of other envelope shapes, suchas tubular or spherical bulbs. The invention is not limited to the lampdescribed and may be used-with halogen incandescent lamps of othervoltage and wattage ratings.

I claim:

1. A halogen-containing incandescent electric lamp having a tungstenmetal filament, said lamp having'an inert fill gas and containing as anadditive in said inert fill gas, at least one perhalogenated hydrocarbonvconv raining 1-4 carbon atoms, said perhalogenated hydrocarboncontaining onlyffluorineand bromine as the halogen atoms and containingat least one fluorine atom-and at least one bromine atom per molecule.

2. Lamp according to claim 1 wherein said hydrocarbon has the formulaCF,,,X, wherein -m is a whole number from 1-3, n is a whole number from1-3, m n equals 4, and X is bromine. i

3. Lamp according to claim 2 wherein said hydrocarbon is added to theinert fill gas in a quantity supplying a concentration of from 7 X 10"to 4 X 10" gram atoms of fluorine per cc of bulb volume and aconcentration of from 7 X 10" to 4 X 10 gram atoms of bromine per cc ofbulb volume.

4. Lamp according to claim 3 wherein said hydrocarbon is CF,Br,.

5. Lamp according to claim 2 wherein said hydrocarbon is at least oneselected from the group consisting of CF Br CF Br, and CFBr 6. Lampaccording to claim 1 wherein said hydrocarbon has the formula C F Xwherein p is a whole number from 1-5, q is a whole number from 1-5, p qequals 6, and X is bromine.

7. Lamp according to claim 6 wherein said hydrocarbon is C F,,l3r and.

8. Lamp according to claim 6 wherein said hydrocarbon is added to theinert fill gas in a quantity supplying a concentration of from 7 X 10 to4 X 10" gram atoms of fluorine per cc of bulb volume and a concentrationof from 7 X 10' to 4 X 10' gram atoms of bromine per cc of bulb volume.

9. Lamp according to claim 1 wherein said hydrocarbon is added to theinert fill gas in a quantity supplying a concentration of from I X 10 tol X 10' gram atoms of fluorine per cc of bulb volume and a concentrationof from 1 X 10- to l X 10' gram atoms of bromine per cc of bulb volume.

2. Lamp according to claim 1 wherein said hydrocarbon has the formulaCFmXn wherein m is a whole number from 1-3, n is a whole number from1-3, m + n equals 4, and X is bromine.
 3. Lamp according to claim 2wherein said hydrocarbon is added to the inert fill gas in a quantitysupplying a concentration of from 7 X 10 8 to 4 X 10 7 gram atoms offluorine per cc of bulb volume and a concentration of from 7 X 10 8 to 4X 10 7 gram atoms of bromine per cc of bulb volume.
 4. Lamp according toclaim 3 wherein said hydrocarbon is CF2Br2.
 5. Lamp according to claim 2wherein said hydrocarbon is at least one selected from the groupconsisting of CF2Br2, CF3Br, and CFBr3.
 6. Lamp according to claim 1wherein said hydrocarbon has the formula C2FpXq wherein p is a wholenumber from 1-5, q is a whole number from 1-5, p + q equals 6, and X isbromine.
 7. Lamp according to claim 6 wherein said hydrocarbon isC2F4Br2 and.
 8. Lamp according to claim 6 wherein said hydrocarbon isadded to the inert fill gas in a quantity supplying a concentration offrom 7 X 10 8 to 4 X 10 7 gram atoms of fluorine per cc of bulb volumeand a concentration of from 7 X 10 8 to 4 X 10 7 gram atoms of bromineper cc of bulb volume.
 9. Lamp according to claim 1 wherein saidhydrocarbon is added to the inert fill gas in a quantity supplying aconcentration of from 1 X 10 8 to 1 X 10 6 gram atoms of fluorine per ccof bulb volume and a concentration of from 1 X 10 8 to 1 X 10 6 gramatoms of bromine per cc of bulb volume.